1. Field of the Invention
The subject matter of this invention is related generally to motor controllers and is related more specifically to microprocessor-controlled motor controllers.
2. Description of the Prior Art
Motor controllers or motor starters as they are sometimes called are well known in the art. Generally, they comprise a switch or ganged switches which are operable to open or close to provide or interrupt current to the stator windings, for example, of an electric motor. The opening and closing process is controlled by appropriately arranged relay coils and relay contacts in what is well known in the prior art as a "relay ladder" arranged in a logical order to properly sequence the starting and/or stopping of the motor.
With the advent of the microprocessor it was found that part, if not all of the relay logic arrangement, could be replaced by a properly programmed microprocessor. Such arrangements are shown and described in a paper entitled "A Quantative Analysis of Grouped Single-Phase Induction Motors" published on page 125 of the IEEE Transactions on Industry Applications, Vol. 1A-17 No. 2, March/April 1981 by J. R. Dunki-Jacobs and Robert H. Kerr; a paper entitled "Thermal Tracking-A Rational Approach to Motor Protection" by D. R. Boothman, E. C. Elgar, R. H. Rehder and R. J. Wooddall identified as IEEE Transactions Paper 274029-5 recommended for presentation at the IEEE PES Winter Meeting, New York, N.Y., Jan. 27-Feb. 1, 1974; a paper entitled "Microprocessor-Based Universal Motor Protection System" appearing in the IEEE Transactions on Industry Applications, Vol. 1A-17 No. 1, January/February 1981 by E. B. Turner and H. Michael Willey and in a descriptive bulletin (41-560(E)) entitled MOTOGARD.TM. for motor protection by the Westinghouse Canada Switchgear and Control Division issued January 1980. A reading of all of the above will show that certain factors are of importance when discussing motor starters or motor controllers.
Since microprocessor-based motor controllers often utilize power derived from the line they are to protect as a power supply for the memories and static devices of the microprocessor in known microprocessor controllers such as the type described in U.S. patent application Ser. No. 339,610 entitled "Motor Control Apparatus With True RMS Non-Sinusoidal Negative Sequence Stator Current Protection Mode", filed Jan. 15, 1982, momentary disruption of the voltage on the lines being monitored can provide a false indication of loss of power. Generally, a microprocessor in this situation will utilize a routine to reset the microprocessor to an initialization point and cause the motor controller contacts to open. This may be viewed as a failsafe type of operation which is more desirable than having the microprocessor function in a garbled manner, but less desirable than having the motor controller contacts open when such is not necessarily required. It will be advantageous therefore if apparatus could be found which could be utilized to determine if a short term power outage should lead to a reinitialization of the microprocessor program and opening of the motor controller contacts.